Tag: physics

Quizzes (598) Questions (13441)

Questions Related to physics

Multiple choice physics some natural phenomena lightning conductors lightning safety advanced of lightning

                      is engineered to protect an elevated structure in the event of lightning strike.

  1. A lightning conductor

  2. Copper wire

  3. A lightening shield

  4. All of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A lightening conductor is a metal rod mounted on a structure and designed to protect the structure from lightening strike. 

Multiple choice physics some natural phenomena lightning conductors lightning safety advanced of lightning

If the instantaneous current in a metallic wire is $i = \left( {5 + 10t} \right)A$ then find amount of charge flown through it from $t = 2s$ to $t = 3s$ is

  1. 10 C

  2. 20 C

  3. 30 C

  4. 40 C
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Given instantaneous current,

$i=(5+10t)A$
and from the definition of instantaneous current,  $i=\dfrac { dq }{ dt } $
$\Rightarrow \quad \left( 5+10t \right) =\dfrac { dq }{ dt } $
$dq=\left( 5+10t \right) dt$
Integrating implies,
$Q=5t+{ 5t }^{ 2 }$
At $t=2$,
                ${ Q } _{ 1 }=30C$
At $t=3$,
                ${ Q } _{ 2 }=60C$

$\therefore $  Option (C) is the correct option.

Multiple choice conduction in metals and non-metals thermal energy transfers physics

Two walls of thickness $d _1$ and $d _2$, thermal conductivities $K _1$ and $K _2$ are in contact. In the steady state if the temperature at the outer surfaces are $T _1$ and $T _2$, the temperature are the common wall will be 

  1. $\dfrac{K _1T _1+K _2T _2}{d _1d _2}$

  2. $\dfrac{K _1T _1d _2+K _2T _2d _1}{K _1d _2+K _2d _1}$

  3. $\dfrac{K _1d _1T _1+K _2d _2T _2}{K _1d _1+K _2d _2}$

  4. $\dfrac{(K _1d _1+K _2d _2)T _1T _2}{T _1+T _2}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$\begin{array}{l} { k _{ 1 } }\dfrac { { { T _{ 1 } }-{ T _{ c } } } }{ { { d _{ 1 } } } } ={ k _{ 2 } }\dfrac { { { T _{ c } }-{ T _{ 2 } } } }{ { { d _{ 2 } } } }  \ where\, { T _{ c } }\, is\, \, common\, \, wall\, temperature,\, solving\, for\, \, { T _{ c } }\, we\, \, will\, get \ { T _{ C } }=\dfrac { { { T _{ 1 } }+\alpha { T _{ 2 } } } }{ { \alpha +1 } }  \ u\sin  g\, \, \alpha =\dfrac { { { d _{ 1 } } } }{ { { d _{ 2 } } } } \dfrac { { { k _{ 2 } } } }{ { { k _{ 1 } } } }  \ { T _{ c } }=\dfrac { { { T _{ 1 } }+\dfrac { { { d _{ 1 } } } }{ { { d _{ 2 } } } } \dfrac { { { k _{ 2 } } } }{ { { k _{ 1 } } } } { T _{ 2 } } } }{ { \dfrac { { { d _{ 1 } } } }{ { { d _{ 2 } } } } \dfrac { { { k _{ 2 } } } }{ { { k _{ 1 } } } } +1 } }  \ =\dfrac { { { T _{ 1 } }\left( { { d _{ 2 } }{ k _{ 1 } } } \right) +{ T _{ 2 } }{ d _{ 1 } }{ k _{ 2 } } } }{ { { d _{ 1 } }{ k _{ 2 } }+{ d _{ 2 } }{ k _{ 1 } } } }  \ Hence,\, the\, option\, B\, is\, the\, \, correct\, answer. \end{array}$

Multiple choice conduction in metals and non-metals thermal energy transfers physics

The area of cross - section of rod is given by $ A = a _0 (1 + \alpha x )  $ where $  A _{ 0 }\quad & \quad \alpha  $ are constant and x is the distance from one end If thermal conductivity of material is K. What is the thermal resistance of the rod if its length is 

  1. $ KA _{ 0 }\alpha \quad to\quad (1+a\ell _{ 0 }) $

  2. $ \frac { 1 }{ Ka _{ 0 }\alpha } \quad \ell n \quad (1+\alpha\ell _{ 0 })$

  3. $ \frac { \alpha }{ KA _{ 0 } } \quad \ell n\quad (1+a\ell _{ 0 }) $

  4. $ \frac { KA _{ 0 } }{ \alpha } \ell n(1+\alpha \ell _{ 0 })$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$\begin{array}{l} A={ a _{ 0 } }\left( { 1+\alpha x } \right)  \ dR=\dfrac { { dx } }{ { KA } }  \ =\dfrac { { dx } }{ { K{ \alpha _{ 0 } }\left( { 1+\alpha x } \right)  } }  \ =R=\dfrac { 1 }{ { K{ a _{ 0 } } } } \int _{ 0 }^{ { l _{ 0 } } }{ \dfrac { { dx } }{ { 1+\alpha x } }  }  \ =\dfrac { 1 }{ { \alpha K{ a _{ 0 } } } } \ln { \left( { 1+\alpha { l _{ 0 } } } \right)  }  \ =\dfrac { 1 }{ { K{ a _{ 0 } }\alpha  } } \ln { \left( { 1+\alpha { l _{ 0 } } } \right)  }  \ Hence, \ option\, \, B\, \, is\, correct\, \, answer. \end{array}$

Multiple choice conduction in metals and non-metals thermal energy transfers physics

a container that suits the occurrence of an isothermal process should be made of 

  1. Copper

  2. Glass

  3. Wood

  4. Cloth
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

An isothermal process requires the system to maintain a constant temperature. A good thermal conductor like copper allows heat to flow easily between the system and the surroundings to maintain that temperature.

Multiple choice conduction in metals and non-metals thermal energy transfers physics

The temperature of skin is $T _{skin} = 34^0C$ (somewhat less than the body temperature, $T _{body} = 37^0C$) and the ambient tempreature is $T _{room} = 24^0C$. The surface area of an adult is A $\simeq$ 1.85 $m^2$. Calculate the net heat loss of the person.

  1. 25 W

  2. 100 W

  3. 300 W

  4. 500 W
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Heat loss can be estimated using Newton's Law of Cooling or basic heat transfer principles. Given the temperature difference (34-24 = 10 degrees) and surface area, the power loss is roughly 25-100W depending on the heat transfer coefficient. 25W is a common textbook answer for this specific problem setup.

Multiple choice conduction in metals and non-metals thermal energy transfers physics

Consider a compound slab consisting of two different materials having equal thickness and thermals conductivities K and $2K$ in series. The equilvalent conductivity of  the slab is

  1. $\frac{2}{3}K$

  2. $\sqrt {2K} $

  3. $3K$

  4. $\left( {\frac{4}{3}} \right)K$
Reveal answer Fill a bubble to check yourself
C Correct answer